The so-called “alumite (registered trademark) method” is known as disclosed by Japanese Patent Application Laid-Open Publication No. H09-176892, in which an oxide film of a predetermined thickness is artificially generated on a base surface of aluminum, for example. According to this method, an electrolytic solution having a strong acid property such as sulfuric acid and oxalic acid is received in an electrolytic vessel, an aluminum-made object to be treated is received in the electrolytic solution, and an oxide film is formed on the base surface of the aluminum by oxidation reaction with the electrolytic solution serving the object as an anode.
However, this conventional oxide film generating method has such problems that an electrolytic solution having a strong acid property such as sulfuric acid and oxalic acid is required, a special water discharging equipment is required for discharging the electrolytic solution, thus increasing the production cost and equipment cost, and operation is obliged to be conducted under such a circumstance that a toxic gas is generated.
Moreover, in case an oxide film having a high degree of hardness is to be generated, the temperature of the electrolytic vessel must be set to low, and in order to prevent increased in temperature due to heat radiation at the time of growth of the oxide film, a cooling equipment and its cooling operation are required. Thus, the production cost and the equipment cost are increased, and productivity is bad.
On the other hand, the above-mentioned oxide film comprises a porous bulk layer, and a barrier layer composed of an amorphous alumina (Al2O3). Of those components, the bulk layer on the outer surface side has a plurality of fine holes formed therein. By infiltrating dye in those fine holes, those areas are dyeable. After dyed, sealing treatment for sealing the holes is carried out, so that the surface of the oxide film is enhanced in corrosion resistance and stain-proof property.
However, the above-mentioned sealing treatment has such problems that an additional treatment vessel is separately required from the anodic oxidation treatment vessel, an object to be treated must be shifted to another vessel after the anodic oxidation is carried out, a pressurized water vapor must be supplied to the treatment vessel or the water received in the treatment vessel must be heated to about 100 degrees C., and a sealing agent such as nickel acetate must be applied thereto, thereby the equipment cost is increased and the process becomes complicated.
It is, therefore, a main object of the present invention to provided, in order to solve the above-mentioned problems, an anodic oxidation method and a treatment apparatus thereof which is suitable, for example, for generation of an oxide film and electropolishing of aluminum, capable of generating an oxide film at a low cost and rapidly eliminating the use of electrolytic solution having a strong acid property and using a carbonated water as the electrolytic solution, and capable of improving the oxide film generating operation and rationalizing the water discharging treatment.
Another object of the present invention is to provide an anodic oxidation method and a treatment apparatus thereof which is capable of preventing increase in temperature of the electrolytic solution without a need of a special equipment, capable of generating an oxide film in a stable manner and obtaining a good oxide film by eliminating the generation of oxygen in the vicinity of an object to be treated.
A further object of the present invention is to provide an anodic oxidation method and a treatment apparatus thereof which is capable of rationalization of the oxide film generating treatment and enhancing the productivity by using supercritical carbon dioxide.